Oxynitride-based fluorescent material and method for production thereof

ABSTRACT

An oxynitride-based fluorescent material is formed of what results from substituting Eu for part of M of a general formula M 3 Si 2 N 2 O 4 , wherein M denotes one or more elements selected from among Be, Mg, Ca, Sr and Ba. The oxynitride-based fluorescent material can be produced by a method comprising mixing an oxide of Be, Mg, Ca, Sr, Ba or Eu, or a compound of Be, Mg, Ca, Sr, Ba or Eu enabled by heating to form an oxide, silicon nitride or a compound enabled by heating to form silicon nitride, and silicon oxide or a compound enabled by heating to form silicon oxide to obtain a mixture and firing the mixture in a vacuum or a non-oxidizing atmosphere at 1200 to 1900° C.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111(a)claiming the benefit pursuant to 35 U.S.C. §119(e)(1) of the filingdates of Provisional Applications No. 60/617,072 filed Oct. 12, 2004 andJapanese Applications No. 2004-284018 filed Sep. 29, 2004 pursuant to 35U.S.C §111(b).

TECHNICAL FIELD

This invention relates to an oxynitride-based fluorescent materialoptically activated with a rare earth element. More particularly, thisinvention relates to an oxynitride-based fluorescent material which iscapable of imparting enhanced luminance to a white light-emitting diode(white LED) using a blue light-emitting diode (blue LED) or anultraviolet light-emitting diode (ultraviolet LED) as the light source.

BACKGROUND ART

The light-emitting diode (LED) is a semiconductor solid-statelight-emitting device formed by joining a p-type semiconductor and ann-type semiconductor. The LED has been serving as the light source forvarious kinds of devices because it possesses strong points, such as along service life, an excellent shock resistance, a lower powerconsumption and high reliability, and moreover permits a reduction involume, thickness and light. Particularly, the white LED is now used forwarning illuminations which are expected to be reliable, on-vehicleilluminations and liquid crystal backlights which are preferred topromise reduction in volume and weight, and railroad guide plates whichare necessitated to ensure visual recognition. It is also expected tofind application to general household indoor illuminations.

When an electric current is fed in the forward direction to the p-njunction formed of a direct transition type semiconductor, the electronsand the holes are combined and the light having a peak wavelengthcorresponding to the forbidden band width of the semiconductor isemitted. Since the emission spectrum of the LED generally has a narrowhalf-band width of the peak wavelength, the luminescent color of thewhite LED is acquired exclusively by the principle of the color mixtureof light.

For the production of a white color, specifically the following methodshave been known.

(1) A method which consists in combining three kinds of LEDs emittingthe three primary colors of light, i.e. red color (R), green color (G)and blue color (B), respectively, and mixing the lights of these LEDs.

(2) A method which consists in combining an ultraviolet LED emitting anultraviolet light and three kinds of fluorescent materials emitting thefluorescences of red color (R), green color (G) and blue color (B),respectively, in response to the excitation by the ultraviolet light andmixing the fluorescences of the three colors emitted from thefluorescent materials.

(3) A method which consists in combining a blue LED emitting a bluelight and a fluorescent material emitting a yellow fluorescence havingthe relationship of a complementary color with the blue light and mixingthe blue LED light and the yellow light emitted from the fluorescentmaterial.

A method which obtains a prescribed luminescent color by using aplurality of LEDs necessitates a special circuit for regulating theelectric currents of the individual LEDs for the purpose of balancingthe relevant colors. In contrast thereto, a method which obtains aprescribed luminescent color by combining an LED and a fluorescentmaterial is at an advantage in obviating the necessity for such acircuit and allowing a reduction in the cost of the LED. Regarding thefluorescent materials of the kind utilizing the LED as a light source,various proposals have been made to date.

For example, a YAG fluorescent material having a YAG-based oxide hostcrystal represented by the constitutional formula, (Y, Gd)₃(Al, Ga)₅O₁₂,doped with Ce has been disclosed (refer to Takashi Mukai et al, AppliedPhysics, Vol. 68, No. 2 (1999), pp. 152-155). This prior art describesthe fact that when the first surface of an InGaN-based blue LED chip iscoated with a thin layer of a YAG fluorescent material, the blue lightemitted from the blue LED and the fluorescence of a peak wavelength of550 nm emitted from the YAG fluorescent material in response to theexcitation by the blue light are mixed to give rise to a white light.

Then, a white LED combining a light-emitting device, such as anitride-based compound semiconductor capable of emitting an ultravioletlight, and fluorescent materials emitting lights in response to theexcitation by the ultraviolet light has been disclosed. As thefluorescent materials to be used herein, a compound (Sr, Ca,Ba)₁₀(PO₄)₆C₁₂:Eu emitting a blue light, a compound 3(Ba, Mg,Mn)O8Al₂O₃:Eu emitting a green light and a compound Y₂O₂S:Eu emitting ared light are disclosed (refer to JP-A 2002-203991).

The existing fluorescent materials generally have a weak point that thespectrum intensity is allayed conspicuously when the excitationwavelength surpasses the near ultraviolet zone.

The white LED obtained by coating the first surface of the InGaN-basedblue LED chip with a fluorescent material formed of a YAG-based oxidehas been reputed as incurring difficulty in forming a white LED of highluminance because the excitation energy of the YAG-based oxide which isa fluorescent material and the excitation energy of the blue LED as thelight source do not coincide and the excitation energy is not convertedwith high efficiency.

Further, in the case of the white LED which is formed by combining alight-emitting device, such as a nitride-based compound semiconductorcapable of emitting an ultraviolet light, and a fluorescent materialemitting light in response to the excitation by the ultraviolet light,this white LED has been reputed as incurring difficulty in obtaining awhite color of high luminance because the luminous efficiency of thefluorescent material of the red component is appreciably low as comparedwith that of any other fluorescent material and consequently the mixingratio of this fluorescent material is proportionately large.

This invention is aimed at providing an oxynitride-based fluorescentmaterial which permits impartation of enhanced luminance to a whitelight-emitting diode (white LED) using a blue light-emitting diode (blueLED) or an ultraviolet light-emitting diode (ultraviolet LED) as thelight source and a light-emitting device using the fluorescent material.

The present inventor has pursued a diligent study with a view toaccomplishing the object mentioned above and has consequently found thatan oxynitride-based fluorescent material resulting from substituting Eufor part of M in the general formula M₃Si₂N₂O₄ (wherein M denotes one ormore elements selected from among Be, Mg, Ca, Sr and Ba) possesses astrong absorption band in a wide range extending over ultraviolet tonear ultraviolet to visible light. He has found anew that the white LEDusing the fluorescent material of this invention possesses an excellentlight-emitting property. This invention has been perfected as a result.

DISCLOSURE OF THE INVENTION

The present invention provides as the first aspect thereof anoxynitride-based fluorescent material formed of what results fromsubstituting Eu for part of M of a general formula M₃Si₂N₂O₄, wherein Mdenotes one or more elements selected from among Be, Mg, Ca, Sr and Ba.

In the second aspect of the invention that includes the first aspect,the oxynitride-based fluorescent material has an elemental ratio of Eu/Min a range of 0.01 to 50 at %.

In the third aspect of the invention that includes the first or secondaspect, the oxynitride-based fluorescent material has an averageparticle diameter of 50 μm or less.

In the fourth aspect of the invention that includes any one of the firstto third aspects, the oxynitride-based fluorescent material has abivalent europium ratio of 50% or more.

In the fifth aspect of the invention that includes any one of the firstto fourth aspects, the oxynitride-based fluorescent material has abivalent europium ratio of 80% or more.

The invention further provides as the sixth aspect thereof a method forthe production of the oxynitride-based fluorescent material according toany one of the first to fifth aspects, which method comprises mixingoxides of Be, Mg, Ca, Sr, Ba and Eu, or compounds of Be, Mg, Ca, Sr, Baand Eu enabled by heating to form oxides, silicon oxide or a compoundenabled by heating to form silicon oxide, and silicon nitride or acompound enabled by heating to form silicon nitride to obtain a mixtureand firing the mixture in a vacuum or a non-oxidizing atmosphere at atemperature of 1200 to 1900° C.

The invention further provides as the seventh aspect thereof a methodfor the production of the oxynitride-based fluorescent materialaccording to any one of the first to fifth aspects, which methodcomprises mixing oxides of Be, Mg, Ca, Sr, Ba and Eu, or compounds ofBe, Mg, Ca, Sr, Ba and Eu enabled by heating to form oxides, siliconoxide or a compound enabled by heating to form silicon oxide, andsilicon nitride or a compound enabled by heating to form silicon nitrideto obtain a mixture and firing the mixture in a presence of carbon or acarbon-containing compound in a vacuum or a non-oxidizing atmosphere ata temperature of 1200 to 1900° C.

The invention further provides as the eighth aspect thereof a method forthe production of the oxynitride-based fluorescent material according toany one of the first to fifth aspects, which method comprises mixingoxides of Be, Mg, Ca, Sr, Ba and Eu, or compounds of Be, Mg, Ca, Sr, Baand Eu enabled by heating to form oxides, silicon oxide or a compoundenabled by heating to form silicon oxide, silicon nitride or a compoundenabled by heating to form silicon nitride, and a seed of theoxynitride-based fluorescent material that is a final syntheticsubstance to obtain a mixture and firing the mixture in a vacuum or anon-oxidizing atmosphere at 1200 to 1900° C.

The invention further provides as the ninth aspect thereof a method forthe production of the oxynitride-based fluorescent material according toany one of the first to fifth aspects, which method comprises mixingoxides of Be, Mg, Ca, Sr, Ba and Eu, or compounds of Be, Mg, Ca, Sr, Baand Eu enabled by heating to form oxides, silicon oxide or a compoundenabled by heating to form silicon oxide, silicon nitride or a compoundenabled by heating to form silicon nitride, and a seed of theoxynitride-based fluorescent material that is a final syntheticsubstance to obtain a mixture and firing the mixture in a presence ofcarbon or a carbon-containing compound in a vacuum or a non-oxidizingatmosphere at 1200 to 1900° C.

The invention further provides as the tenth aspect thereof alight-emitting apparatus combining the oxynitride-based fluorescentmaterial according to any one of the first to fifth aspects and alight-emitting element.

In the eleventh aspect of the invention that includes the tenth aspect,the light-emitting device is a nitride-based semiconductorlight-emitting device, an emission wavelength of which is in a range of250 nm to 500 nm.

The fluorescent material of this invention can be effectively applied tothe operations of a white LED using an ultraviolet LED or a blue LEDbecause it possesses an absorption band of a wide range extending overultraviolet to near ultraviolet to visible light. It can enhance theluminance of the white LED because it has a strong absorption band.

The above and other objects, characteristic features and advantageous ofthe present invention will become apparent to those skilled in the artfrom the description to be made herein below with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the emission wavelength and the emissionintensity which are obtained by exciting the fluorescent material ofthis invention by the use of a light-emitting diode.

BEST MODE FOR CARRYING OUT THE INVENTION

The oxynitride fluorescent material of this invention, as describedabove, is an oxynitride-based fluorescent material formed of what hassubstituted Eu for part of M of the general formula M₃Si₂N₂O₄, wherein Mdenotes one or more members selected from among Be, Mg, Ca, Sr and Ba.Such compounds as Be₃Si₂N₂O₄, Mg₃Si₂N₂O₄, Ca₃Si₂N₂O₄, Sr₃Si₂N₂O₄,Ba₃Si₂N₂O₄, (Be_(a), Mg_(b), Ca_(c), Sr_(d), Ba_(e))₃Si₂N₂O₄ (whereina+b+c+d+e=1 and 0≦a<1, 0≦b<1, 0≦c<1, 0≦d<1 and 0≦e<1) may be cited asconcrete examples thereof Among other compounds enumerated above,Mg₃Si₂N₂O₄, Ca₃Si₂N₂O₄, Sr₃Si₂N₂O₄, Ba₃Si₂N₂O₄, (Mg_(a), Ca_(b), Sr_(c),Ba_(d))₃Si₂N₂O₄ (wherein a+b+c+d+e=1, 0≦a<1, 0≦b<1, 0≦c<1 and 0≦d<1) arepreferable. The amount of Eu used for the substitution is preferably inthe range of 0.01 to 50 at % (atom %). The average particle diameter ofthe fluorescent material is preferably 50 μm or less.

As the raw material compound for the oxynitride-based fluorescentmaterial, the oxide of one or more members selected from the groupconsisting of Be, Mg, Ca, Sr and Ba or the compound of one or moremembers selected from the group consisting of Be, Mg, Ca, Sr and Ba andenabled by heating to form the oxide. As concrete examples of the rawmaterial compound, beryllium oxide, magnesium oxide, calcium oxide,strontium oxide, barium oxide, beryllium carbonate, magnesium carbonate,calcium carbonate, strontium carbonate, barium carbonate, berylliumhydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide,barium hydroxide, beryllium oxalate, magnesium oxalate, calcium oxalate,strontium oxalate, barium oxalate, beryllium sulfate, magnesium sulfate,calcium sulfate, strontium sulfate, barium sulfate, beryllium nitrate,magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate,beryllium acetate, magnesium acetate, calcium acetate, strontiumacetate, barium acetate, dimethoxy beryllium, dimethoxy magnesium,dimethoxy calcium, dimethoxy strontium, dimethoxy barium, diethoxyberyllium, diethoxy magnesium, diethoxy calcium, diethoxy strontium,diethoxy barium, dipropoxy beryllium, dipropoxy magnesium, dipropoxycalcium, dipropoxy strontium, dipropoxy barium, dibutoxy beryllium,dibutoxy magnesium, dibutoxy calcium, dibutoxy strontium, dibutoxybarium, bis(dipivaloyl methanite) beryllium, bis(pivaloyl methanite)magnesium, vis(dipivaloyl methanite) calcium, bis(dipivloyl methanite)strontium, and bis(dipivloyl methanite) barium may be cited. One rawmaterial compound selected from the group consisting of the compoundsenumerated above may be used. A mixture, a complex oxide, a solidsolution or a mixed crystal formed of two or more members selected fromthis group may be also used. Of these compounds, a carbonate orhydroxide is preferable, and what is particularly preferable is acarbonate.

Then, as the raw material compound of Eu, the oxide of Eu or thecompound of Eu enabled by heating to form the oxide can be used. Forexample, one or more members selected from among europium oxide,europium carbonate, europium hydroxide, europium oxalate, europiumsulfate, europium nitrate, europium acetate, trimethoxy europium,triethoxy europium, tripropoxy europium and tributoxy europium may beused. A mixture, a complex oxide, a solid solution or a mixed crystalformed of two or more members selected from this group may be also used.

As the raw material compound for silicon oxide, silicon oxide or acompound enabled by heating to form silicon oxide can be used. Forexample, one or more members selected from among silicon dioxide,silicon monoxide, tetramethoxy silane, tetraethoxy silane, tetrapropoxysilane, tetrabutoxy silane and tris(dimethylamino) silane may be used. Amixture, a solid solution or a mixed crystal formed of two or moremembers thereof can also be used.

As the raw material compound of silicon nitride, silicon nitride or acompound enabled by heating to form silicon nitride can be used. One ormore members selected from among silicon diimide, polysilazane, etc. canbe used. A similar result may be obtained by mixing one or morecompounds selected from among silicon, silicon dioxide, siliconmonoxide, tetramethoxy silane, tetraethoxy silane, tetrapropoxy silane,tetrabutoxy silane and tris(dimethylamino) silane optionally with carbonor a compound enabled by heating to form carbon and heating theresultant mixture in nitrogen or a nitrogen-containing non-oxidizingatmosphere. Of these materials, those in the form of a solid state arepreferably pulverized into powder. Though the degree of particle sizethere of does not need to be particular restricted, finely pulverizedpowder is preferred because of excellence in reactivity. The purity of90% or more is preferred.

The method for producing the oxynitride fluorescent material does notneed to be particularly restricted. Any of the solid phase method,liquid phase method and vapor phase method may be adopted for theproduction. In the case of the solid phase production, the followingmethod may be cited.

For a start, the raw material compounds are weighed out in desiredratios and mixed. A ball mill can be used when this mixing is performed.Though a dry-mixing can be adopted when using a ball mill, a wet-mixingusing ethanol, acetone, water, etc. can also be adopted. In order toenhance the reactivity of the raw material powder, the wet-mixing isdesirable. When adopting the wet-mixing, mixed slurry obtained is driedand, when necessary, pulverized. At this point, the selected rawmaterial compounds may be mixed with a flux which is optionally added.As the flux, the halogenide of an alkali metal or the halogenide of analkaline earth metal can be used. It is added, for example, in an amountin the range of 0.01 to 1 part by weight based on 100 parts by weight ofthe raw material compounds of the fluorescent material.

A powdered oxynitride-based fluorescent material synthesized in advancemay optionally be added to and mixed with the raw material compounds.The amount thereof to be added is in the range of 1 to 50 parts byweight based on 100 parts by weight of the raw material compounds of thefluorescent material.

The resultant raw material mixture is packed in a crucible made ofalumina, calcia, magnesia, graphite or boron nitride and fired in avacuum or a non-oxidizing atmosphere at 1200 to 1900° C. for severalhours. The non-oxidizing atmosphere, when necessary, may be pressed.Here, the non-oxidizing atmosphere is referred to an atmosphere ofnitrogen, nitrogen-hydrogen, ammonium, argon, etc.

In the fluorescent material of this invention, europium exhibits idealemission when it is in the form of plus bivalence. Since the europiumoxide which is used as the raw material is trivalent, it must be reducedby the process of firing. The ratio of the bivalence and the trivalencegains in preferability in accordance as the bivalence increases. Theratio of the bivalence to the whole europium is preferably 50% or more.It is more preferably 80% or more. In the fluorescent material of thisinvention, since europium is added by replacing the site of a bivalentalkaline earth metal, the residue of trivalent europium, if any, willdisrupt the balance of electric charge and induce degradation of theintensity of emission. The ratio of the bivalent europium and trivalenteuropium can be analyzed by the Moessbauer spectroscopy.

When the raw material mixture is fired in the presence of carbon or acarbon-containing compound, the reduction of europium oxide isexpedited. The carbon or the carbon-containing compound which is usedherein does not need to be particularly restricted but is required to beamorphous carbon, graphite or silicon carbide, for example. It ispreferably amorphous carbon or graphite. Carbon black, powderedgraphite, activated carbon, powdered silicon carbide, molded productsthereof and sinters thereof may be cited as concrete examples. The sameeffect can be obtained from any of these. As regards the mode of thepresence, the case of using a crucible which is made of carbon or acarbon-containing compound, the case of having carbon or acarbon-containing compound disposed inside or outside a crucible whichis made of a material other than carbon or a carbon-containing compound,and the case of using a heating unit or an insulating unit which is madeof carbon or a carbon-containing compound may be cited as concreteexamples. These methods of disposition bring the same effect, no matterwhich of them may be actually adopted. The carbon or thecarbon-containing compound intended for the presence is usedappropriately in an amount approximately equimolar to the amount ofeuropium oxide in the raw material mixture when powdered carbon iscontained in the raw material mixture and this mixture is fired in anatmosphere of nitrogen, for example.

The product of the firing is cooled, then optionally subjected to adispersing and pulverizing treatment with a ball mill, further subjectedoptionally to a treatment of water washing, and passed through the stepsof solid-liquid separation, drying, crushing and classification to giverise to the fluorescent material of this invention.

The fluorescent material of this invention is excited fully efficientlywith an ultraviolet light or a visible light having a wavelength in therange of 250 nm to 500 nm and, therefore, can be effectively applied tothe white LED services using an ultraviolet LED or a blue LED.

The fluorescent material which is one preferred embodiment of thisinvention may be combined with a semiconductor light-emitting devicewhich emits light in a wavelength zone from 250 nm through 500 nm toconfigure a light-emitting apparatus. In this case, as thelight-emitting device various semiconductor, such as of ZnSe or GaN canbe cited. It can be used infinitely so long as it is capable of emittinglight at an emission spectrum in the range of 250 nm through 500 nm.From the viewpoint of efficiency, the gallium nitride-basedsemiconductor light-emitting elements are preferably used. Thelight-emitting device can be obtained by depositing a galliumnitride-based semiconductor on a substrate using the MOCVD method, HVPEmethod, etc. Preferably, In_(α)Al_(β)Ga_(1-α-β)N (wherein 0≦α, 0≦β andα+β≦1) is used as a light-emitting layer. As regards the structure ofthe semiconductor, the homostructures possessing a MIS junction, a PINjunction or a p-n junction, the heterostuctures, and the doubleheterostructures may be cited. A varying emission wavelength can beselected, depending on the material of a semiconductor layer and thedegree of mixed crystal thereof. The single quantum well structurehaving a semiconductor active layer formed in a thin film generating aquantum effect and the multiple quantum well structure are similarlyavailable.

The aforementioned fluorescent material layer to be disposed on thelight-emitting device may result from having at least one kind of afluorescent material deposited in a single layer or stacked in aplurality of layers or having plural kinds of fluorescent materialsdisposed as mixed in a single layer. As concrete examples of the mode ofdisposing the fluorescent material layer on the aforementionedlight-emitting device, the mode of having the fluorescent materialincorporated in advance in the coating member destined to coat the firstsurface of the light-emitting device, the mode of having the fluorescentmaterial incorporated in the molding member, the mode of having thefluorescent material incorporated in advance in the coating materialdestined to cover the molding member, and further the mode of disposinga transparent plate having the fluorescent material incorporated inadvance therein in front of the light-projecting side of the LED lampmay be cited.

The aforementioned fluorescent material may have at least one kind offluorescent material incorporated in advance in the mold member on thelight-emitting device. Further, the aforementioned fluorescent materiallayer formed of at least one kind of fluorescent material may bedisposed on the outside of the light-emitting diode. As concreteexamples of the mode of disposing the fluorescent material layer on theoutside of the light-emitting diode, the mode of applying thefluorescent material in the form of a layer to the outer side surface ofthe mold member of the light-emitting diode, the mode of preparing amolded material (as in the shape of a cap) having a fluorescent materialdispersed in rubber, resin, elastomer or a low-melting glass and coatingthe LED with this molded material, and the mode of converting the moldedmaterial mentioned above into a flat plate and disposing this flat platein front of the LED may be cited.

Also, the mold member may have incorporated therein diffusion agents,such as titanium oxide, titanium nitride, tantalum nitride, aluminumoxide, silicon oxide, barium titanate, germanium oxide, mica, hexagonalboron nitride, or mica coated with white powder of titanium oxide,aluminum oxide, silicon oxide, barium titanate, germanium oxide orhexagonal boron nitride, or hexagonal boron nitride coated with whitepowder of titanium oxide, aluminum oxide, silicon oxide, bariumtitanate, germanium oxide, etc.

This invention will be explained below with reference to examples. Thisinvention is not limited to the examples. Incidentally, in the followingexamples, the emission spectra were determined by an instrument made byNippon Bunko K.K. and sold under the product code of “FP-6500.”

Example 1

As component raw materials for a fluorescent material, 4.82 g ofpowdered europium oxide, 5.49 g of powdered silicon oxide, 12.82 g ofpowdered silicon nitride, and 76.83 g of powdered strontium carbonatewere accurately weighed out and they were uniformly mixed with a ballmill by the wet method using ethanol to obtain slurry. The slurry isdried and crushed to give rise to a raw material mixture. Then, theresultant raw material mixture was placed in a crucible made ofgraphite, then disposed in a reactor core tube and fired therein in acurrent of nitrogen at a temperature of 1550° C. for six hours. Theresultant fired material was finely pulverized with a ball mill andclassified to give rise to a fluorescent material having an averageparticle diameter of 4.5 μm. When this fluorescent material was examinedwith an X-ray diffractometer and an electron beam microanalyzer, it wasidentified as Sr_(2.85)Eu_(0.15)Si₂N₂O₄. When this fluorescent materialwas excited at 380 nm to emit light, it was found to emit light of acolor corresponding to yellowish orange. The emission spectrum of thisfluorescent material is shown in FIG. 1. In FIG. 1, the horizontal axisis the scale of emission wavelength (nm) of the fluorescent material andthe vertical axis the scale of the emission spectrum intensity(arbitrary scale).

Example 2

When the fluorescent material obtained in Example 1 was excited at 450nm to emit light, it was found to emit light of a color corresponding toyellow.

Example 3

The fluorescent material obtained in Example 1 was mixed in a ratio of20 mass % with silicone rubber. The resultant mixture was molded in theshape of a cap with a heating press. When this cap was so disposed as tocover the outside of a near ultraviolet LED having an emissionwavelength of 380 nm and caused to emit light, it was found to emitlight of a color corresponding to yellowish orange. Even after the LEDhad been lit for 500 hours under the conditions of 60° C. of temperatureand 90% of RH (relative humidity), no change ascribable to thefluorescent material was recognized.

Example 4

A white LED manufactured by mixing the fluorescent material obtained inExample 1 and Sr₅(PO₄)₃Cl:Eu as a blue light-emitting fluorescentmaterial in respective ratios of 5.7 mass % and 9.0 mass % in siliconerubber and mounting the resultant mixture on a 380-nm near ultravioletlight emitting device and a white LED manufactured by mixing Y₂O₂S:Eu asa red light-emitting fluorescent material, Sr₅(PO₄)₃Cl:Eu as a bluelight-emitting fluorescent material, BaMg₂Al₁₆O₂₇:Eu, Mn as a greenlight-emitting fluorescent material in respective ratios of 45.8 mass %,3.8 mass % and 3.4 mass % and mounting the resultant mixture on a 380-nmnear ultraviolet light-emitting device were compared. Consequently, thesample using the fluorescent material obtained in Example 1 andSr₅(PO₄)₃Cl:Eu as a blue light-emitting fluorescent material was foundto produce white light possessing 1.8 times as high luminance as theother sample.

Example 5

A white color LED was manufactured by mixing the fluorescent materialobtained in Example 1 in a ratio of 9.1 mass % in epoxy resin andmounting the resultant mixture on a 450-nm blue light-emitting device.The white light emitted by this white LED was found to have a luminousefficiency of 36 (lm/W).

Example 6

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,3.83 g of powdered europium oxide, 4.36 g of powdered silicon oxide,10.18 g of powdered silicon nitride and 81.63 g of powdered bariumcarbonate were accurately weighed out and the firing temperature was setto be 1500° C. When this fluorescent material was excited at 380 nm toemit light, it was found to emit light of a color corresponding tobluish green.

Example 7

When the fluorescent material obtained in Example 6 was excited at 450nm to emit light, it was found to emit light of a color corresponding tobluish green in the same manner as in Example 6.

Example 8

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,4.27 g of powdered europium oxide, 4.86 g of powdered silicon oxide,11.35 g of powdered silicon nitride, 34.03 g of powdered strontiumcarbonate and 45.49 g of powdered barium carbonate were accuratelyweighed out. When the fluorescent material was excited at 450 nm to emitlight, it was found to emit light of a color corresponding to yellowishgreen.

Example 9

When the fluorescent material obtained in Example 8 was excited at 380nm to emit light, it was found to emit light of a color corresponding toyellowish green in the same manner as in Example 8.

Example 10

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,5.14 g of powdered europium oxide, 5.85 g of powdered silicon oxide,13.66 g of powdered silicon nitride, 13.89 g of powdered calciumcarbonate and 61.46 g of strontium carbonate were accurately weighedout. When the fluorescent material was excited at 450 nm to emit light,it was found to emit light of a color corresponding to orange.

Example 11

Where the fluorescent material obtained in Example 10 was excited at 380nm to emit light, it was found to emit light of a color corresponding toorange in the same manner as in Example 10.

Example 12

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,5.50 g of powdered europium oxide, 6.26 g of powdered silicon oxide,14.63 g of powdered silicon nitride, 29.74 g of powdered calciumcarbonate and 43.87 g of powdered strontium carbonate were accuratelyweighed out. When the fluorescent material was excited at 450 nm to emitlight, it was found to emit light of a color corresponding to orangishred.

Example 13

When the fluorescent material obtained in Example 12 was excited at 380nm to emit light, it was found to emit light of a color corresponding toorangish red in the same manner as in Example 12.

Example 14

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,6.41 g of powdered europium oxide, 7.29 g of powdered silicon oxide,17.03 g of powdered silicon nitride and 69.26 g of powdered calciumcarbonate were accurately weighed out. When the fluorescent material wasexcited at 450 nm to emit light, it was found to emit light of a colorcorresponding to red.

Example 15

When the fluorescent material obtained in Example 14 was excited at 380nm to emit light, it was found to emit light of a color corresponding tored in the same manner as in Example 14.

Example 16

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,4.82 g of powdered europium oxide, 5.49 g of powdered silicon oxide,12.82 g of powdered silicon nitride and 76.87 g of powdered strontiumcarbonate were accurately weighed out and uniformly mixed by the drymethod using an agate mortar. When the fluorescent material was excitedat 450 nm to emit light, it was found to emit light of a colorcorresponding to yellowish orange.

Comparative Example 1

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,6.55 g of powdered europium oxide, 7.46 g of powdered silicon oxide,17.41 g of powdered silicon nitride and 68.58 g of powdered strontiumnitride were accurately weighed out and uniformly mixed with a ball millby the wet method using ethanol, the slurry obtained was dried andcrushed to give rise to a raw material mixture. When the fluorescentmaterial was excited at 450 nm, it was found to emit no light.

Comparative Example 2

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,6.55 g of powdered europium oxide, 7.46 g of powdered silicon oxide,17.41 g of powdered silicon nitride and 68.58 g of powdered strontiumnitride were accurately weighed out and uniformly mixed by the drymethod using an agate mortar to give rise to a raw material mixture.When the fluorescent material was excited at 450 nm to emit light, itwas found to emit light of a color corresponding to yellowish orangewhile the emission intensity was 41% as compared with that of thefluorescent material of Example 16.

Comparative Example 3

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,4.82 g of powdered europium oxide, 5.49 g of powdered silicon oxide,12.82 g of powdered silicon nitride and 76.87 g of powdered strontiumcarbonate were accurately weighed out and uniformly mixed with a ballmill by the wet method using ethanol, the slurry obtained was dried andcrushed to give rise to a raw material mixture, which was placed in acrucible made of alumina, then disposed in a reactor core tube and firedtherein in a current of nitrogen at a temperature of 1550° C. for sixhours. When the fluorescent material was excited at 450 nm to emitlight, it was found to emit light of a color corresponding to yellowishorange while the emission strength was 53% as compared with that of thefluorescent material of Example 1.

Comparative Example 4

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,4.82 g of powdered europium oxide, 5.49 g of powdered silicon oxide,12.82 g of powdered silicon nitride, and 76.87 g of powdered strontiumcarbonate were accurately weighed out and uniformly mixed with a ballmill by the wet method using ethanol, the slurry obtained was dried andcrushed to give rise to a raw material mixture, which was placed in acrucible made of boron nitride and disposed in a reactor core tube madeof alumina and fired therein in a current of nitrogen at a temperatureof 1550° C. for six hours. When the fluorescent material was excited at450 nm to emit light, it was found to emit light of a colorcorresponding to yellowish orange while the emission strength was 61% ascompared with that of the fluorescent material of Example 1.

Example 17

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,4.82 g of powdered europium oxide, 5.49 g of powdered silicon oxide,12.82 g of powdered silicon nitride and 76.87 g of powdered strontiumcarbonate were accurately weighed out and uniformly mixed with a ballmill by the wet method using ethanol, the slurry obtained was dried andcrushed to give rise to a raw material mixture, which was placed in acrucible made of alumina and disposed in a reactor core tube made ofalumina together with a graphite piece and fired therein in a current ofnitrogen at a temperature of 1550° C. for six hours. When thefluorescent material was excited at 450 nm to emit light, it was foundto emit light of a color corresponding to yellowish orange and theemission strength was at the same level as in Example 1.

Example 18

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,4.82 g of powdered europium oxide, 5.49 g of powdered silicon oxide,12.82 g of powdered silicon nitride and 76.87 g of powdered strontiumcarbonate were accurately weighed out and uniformly mixed with a ballmill by the wet method using ethanol, the slurry obtained was dried andcrushed to give rise to a raw material mixture, which was placed in acrucible made of alumina together with a graphite piece and disposed ina reactor core tube made of alumina and fired therein in a current ofnitrogen at a temperature of 1550° C. for six hours. When thefluorescent material was excited at 450 nm to emit light, it was foundto emit light of a color corresponding to yellowish orange and theemission strength was at the same level as in Example 1.

Example 19

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,4.82 g of powdered europium oxide, 5.49 g of powdered silicon oxide,12.82 g of powdered silicon nitride and 76.87 g of powdered strontiumcarbonate were accurately weighed out and uniformly mixed with a ballmill by the wet method using ethanol, the slurry obtained was dried andcrushed to give rise to a raw material mixture, which was placed in acrucible made of alumina and disposed in an internal heat-type firingfurnace using a graphite heater and fired therein in a current ofnitrogen at a temperature of 1550° C. for six hours. When thefluorescent material was excited at 450 nm to emit light, it was foundto emit light of a color corresponding to yellowish orange and theemission strength was at the same level as in Example 1.

Example 20

A fluorescent material was obtained by following the procedure ofExample 1 while as component raw materials for a fluorescent material,4.82 g of powdered europium oxide, 5.49 g of powdered silicon oxide,12.82 g of powdered silicon nitride, 76.87 g of powdered strontiumcarbonate and 10.00 g of a target powered oxynitride fluorescentmaterial were accurately weighed out and the firing temperature was setto be 1450° C. When the fluorescent material was excited at 450 nm toemit light, it was found to emit light of a color corresponding toyellowish orange and the emission strength was at the same level as inExample 1.

Example 21

The fluorescent materials obtained in Examples 1, 6, 8, 10, 12 and 14were mixed in respective amounts of 4.7 mass %, 4.0 mass %, 4.7 mass %,8.2 mass %, 12.1 mass % and 17.6 mass % in silicone rubber and mountedon a 380 nm-near ultraviolet light-emitting devices to fabricate whiteLEDs. The white LEDs were compared to find an average color renderingindex of 91.

INDUSTRIAL APPLICABILITY

The combination of the fluorescent material of this invention as with ablue light-emitting diode results in emitting a white light, which canbe utilized as an illuminating light source and a display light source.

1. An oxynitride-based fluorescent material formed of what results fromsubstituting Eu for part of M of a general formula M₃Si₂N₂O₄, wherein Mdenotes one or more elements selected from among Be, Mg, Ca, Sr and Ba.2. An oxynitride-based fluorescent material according to claim 1,wherein it has an elemental ratio of Eu/M in a range of 0.01 to 50 at %.3. An oxynitride-based fluorescent material according to claim 1,wherein it has an average particle diameter of 50 μm or less.
 4. Anoxynitride-based fluorescent material according to claim 1, wherein ithas a bivalent europium ratio of 50% or more.
 5. An oxynitride-basedfluorescent material according to claim 1, wherein it has a bivalenteuropium ratio of 80% or more.
 6. A light-emitting apparatus combiningthe oxynitride-based fluorescent material according to claim 1 and alight-emitting element.
 7. A light-emitting apparatus according to claim6, wherein the light-emitting device is a nitride-based semiconductorlight-emitting device, an emission wavelength of which is in a range of250 nm to 500 nm.
 8. An oxynitride-based fluorescent material accordingto claim 1, wherein a ratio of bivalent europium to the whole europiumis 50% or more.